In the manufacture of paper products, such as tissue products, a wide variety of product characteristics must be given attention in order to provide a final product with the appropriate blend of attributes suitable for the product's intended purposes. Improving the softness of tissues is a continuing objective in tissue manufacture, especially for premium products. Softness is a perceived property of tissues comprising many factors including thickness, smoothness and fuzziness.
Many tissue products and other paper webs are typically formed into large supply rolls after being manufactured. After the supply rolls are formed, the rolls are rewound into smaller sized rolls, which are generally more useful for commercial purposes. For example, in conventional systems, a core is often placed onto a mandrel that is capable of spinning so that the spinning of the mandrel in conjunction with the core can effectuate winding of the paper thereon.
When tissue products, however, are formed into a rolled product during winding and converting, the inner layers of the rolled product may tend to lose a noticeable amount of bulk due to the compressive forces that are exerted on the base web. Lowering bulk can reduce the perceived quality of the product. As such, a need currently exists for a process and system that controls the winding process in order to control bulk reduction.
Another problem experienced in the formation of wound products is in producing multiple rolls of material that all have a diameter and roll firmness within desired limits. Ideally, the rolled products should have a substantially uniform diameter and roll firmness so that there are no consumer noticed differences between the rolls. Further, consumers desire rolled products, especially rolled tissue products, to have a roll firmness within a desired range such that the rolls do not feel too hard or too “mushy”.
The ability to form rolled products having a substantially uniform diameter and roll firmness also provide various other benefits during production of the product. For instance, controlling roll firmness can, in some applications, increase throughput efficiency. Further, uniform products can be easier to package, eliminating or reducing packaging delays that may occur if the rolls were formed with irregular properties.
In the past, one method of measuring roll firmness was to use a Kershaw roll firmness tester as described, for instance, in U.S. Pat. No. 6,077,590 to Archer, et al. which is incorporated herein by reference. The Kershaw roll firmness tester is designed to measure the roll firmness of selected individual cut rolls offline. Unfortunately, once measurements are taken, it is sometimes difficult to use the data for modifying process conditions in order to improve the quality of products produced, due to the delay involved in obtaining the measurement.
As such, a need currently exists for a roll firmness device that is capable of measuring the roll firmness of a roll of material shortly after the roll is formed. A need also exists for a system that can automatically make process adjustments based upon online roll firmness measurements.
Definitions
A tissue product as described in this invention is meant to include paper products made from base webs such as bath tissues, facial tissues, paper towels, industrial wipers, foodservice wipers, napkins, medical pads, and other similar products.
The Kershaw Test is a test used for determining roll firmness. The Kershaw Test is described in detail in U.S. Pat. No. 6,077,590 to Archer, et al., which is incorporated herein by reference. FIG. 5 illustrates the apparatus used for determining Kershaw roll firmness. The apparatus is available from Kershaw Instrumentation, Inc., Swedesboro, N.J., and is known as a Model RDT-2002 Roll Density Tester. Shown is a towel or bath tissue roll 200 being measured, which is supported on a spindle 202. When the test begins a traverse table 204 begins to move toward the roll. Mounted to the traverse table is a sensing probe 206. The motion of the traverse table causes the sensing probe to make contact with the towel or bath tissue roll. The instant the sensing probe contacts the roll, the force exerted on the load cell will exceed the low set point of 6 grams and the displacement display will be zeroed and begin indicating the penetration of the probe. When the force exerted on the sensing probe exceeds a set point, the value is recorded. After the value is recorded, the traverse table will stop and return to the starting position. The displacement display indicates the displacement/penetration in millimeters. The tester may record this reading. Next the tester will rotate the tissue or towel roll 90 degrees on the spindle and repeat the test. The roll firmness value is the average of the two readings. The test needs to be performed in a controlled environment of 73.4±1.8 degrees F. and 50±2% relative humidity. The rolls to be tested need to be introduced to this environment at least 4 hours before testing.